My question is: what will happen with materials appliers and BoM? System layers only allow for a diffuse right? and I assume bodies will have only 1 layer for skin pores/sheen effect. Does this mean we won't be able to have layered clothing with materials? 
yeah.. that's what it appears to be at the moment...
nimil: I'm happy for having BoM back but I'm sad for my shiny stuff!!
i'm hoping it'll get more added as time goes on!
that's been going through my head as well and it made me realize that maybe BOM might not turn into such a big thing as expected. everyone loves their mats
My guess is you'll have to do optional material, unfortunately, you'll have limited materials space and hope the body has one auxiliary onion layer for specialty tattoos that require materials. We'll have to see how bodies tackle this.
Allegory
dice
you can pick one mat layer for spec/norm. so, if latex clothing, no shiny skin, etc. old omega friendly bodies can be used as mixed BoM/applier for layering extra clothing with mats, but you are right back in being the lagmonster, pure BoM is _significantly_ less resource intensive.